The present invention relates to a semiconductor device and a method of manufacturing the same, particularly, to a fine MIS transistor having a short gate length.
A so-called SALICIDE (Self ALIgned siliCIDE) process has come to be used widely in order to cope with an increased parasitic resistance accompanying the miniaturization of the element in recent years. The salicide process is used for forming silicide films on a polycrystalline silicon gate electrode and source-drain regions of a MOSFET by self-alignment.
FIGS. 10A to 10F exemplify a conventional salicide process using titanium.
In the first step, an element isolation region 102 consisting of a silicon oxide film is formed on a silicon substrate 101, followed by forming a gate oxide film 103, a polycrystalline silicon gate electrode 104 and shallow source-drain regions 105 of a MOSFET, as shown in FIG. 10A. Further, deep source-drain diffusion layers 107 are formed by using side wall films 106 each consisting of silicon nitride as a mask.
Then, a treatment with a dilute hydrofluoric acid, followed by, as desired, an RCA treatment, is applied to deposit a titanium film 108 and a titanium nitride (TiN) film 109 on the entire surface, as shown in FIG. 10B.
Further, an annealing treatment is carried out for a short time at 650 to 750.degree. C. by using a lamp annealing apparatus or the like. By this annealing treatment, reactions are carried out between the silicon substrate 101 and the titanium film 108, and the polycrystalline silicon film 104 and the titanium film 108 so as to form a titanium disilicide (TiSi.sub.2) film 110 having a C49 crystal structure. Then, the titanium nitride film 109 and the unreacted titanium film 108 are removed by etching using a mixture of sulfuric acid and hydrogen peroxide as an etchant, as shown in FIG. 10C.
In the next step, an annealing treatment is performed for a short time at 750 to 900.degree. C. by using a lamp annealing apparatus or the like so as to convert the titanium disilicide film 110 having the C49 crystal structure into a titanium disilicide (TiSi.sub.2) film 111 of a low resistivity, said film 111 having a C54 crystal structure, as shown in FIG. 10D. After formation of the titanium disilicide film 111, silicon oxide films 112 and 113 are deposited on the entire surface by a low pressure CVD method and a plasma CVD method, followed by flattening the upper surface of the silicon oxide film 113 by, for example, a CMP (Chemical Mechanical Polishing) process, as shown in FIG. 10E.
Finally, contact holes are made through the silicon oxide films 112 and 113, followed by burying a metal layer 114 such as a tungsten layer in the contact hole. Further, a wiring layer 115 made of, for example, aluminum is formed in a manner to be connected to the source-drain diffusion layers and the gate electrode, as shown in FIG. 10F.
The salicide process using titanium, which is described above, is effective for markedly decreasing the parasitic resistance of the source-drain diffusion layers and the polycrystalline silicon gate electrode. However, if the gate length is decreased to 0.2 .mu.m or less with progress in miniaturization of the element, the crystal structure of the TiSi.sub.2 film is not converted into the C54 crystal structure by the second lamp annealing treatment. As a result, the resistance is not lowered so as to give rise to a so-called narrow line effect and, thus, to diminish the merit produced when the salicide process is employed for the manufacture of a semiconductor device.
Under the circumstances, a salicide process using a cobalt silicide, which is unlikely to bring about the narrow line effect compared with titanium silicide, attracts attentions in recent years.
FIGS. 11A to 11D exemplify the salicide process using cobalt silicide.
In the first step, a treatment with a dilute hydrofluoric acid is applied to the MOSFET under the state of FIG. 10A so as to remove the native oxide film on the surfaces of the silicon substrate 101 and the polycrystalline silicon film 104, followed depositing a cobalt film 116 and a titanium nitride film 109 on the entire surface, as shown in FIG. 11A.
Then, an annealing treatment is performed for a short time at about 450 to 550.degree. C. by using, for example, a lamp annealing apparatus. By this lamp annealing treatment, reactions are carried out between the silicon substrate 101 and the cobalt film 116, and the polycrystalline silicon film 104 and the cobalt film 116 so as to form a cobalt monosilicide (CoSi) film 117. Then, the titanium nitride film 109 and the unreacted cobalt film 116 are removed by etching with an etchant such as a mixed solution consisting of sulfuric acid and hydrogen peroxide, as shown in FIG. 11B.
After the etching step, an annealing treatment is performed for a short time at 700 to 850.degree. C. by using, for example, a lamp annealing apparatus. By this annealing treatment, the cobalt monosilicide film 117 is converted into a cobalt disilicide (CoSi.sub.2) film 118 having a low resistivity, as shown in FIG. 11C.
Further, silicon oxide films 112 and 113 are deposited on the entire surface by a low pressure CVD method and a plasma CVD method, followed by flattening the upper surface of the oxide film 113 by, for example, a CMP method. Still further, contact holes are made through these silicon oxide films 112, 113, followed by burying a metal layer 114 consisting of, for example, tungsten in these contact holes. Finally, a wiring layer 115 made of, for example, aluminum is formed in a manner to be connected to the source-drain diffusion layers and the gate electrode, as shown in FIG. 11D.
The salicide process using a cobalt silicide film, which is described above, is advantageous over the salicide process using a titanium silicide film in that a narrow line effect is unlikely to take place. However, serious problems remain unsolved in the salicide process using a cobalt silicide film, as described in the following.
It should be noted first of all that cobalt is inferior to titanium in the capability of reducing a silicon oxide film. Therefore, where a native oxide film formed after the RCA treatment is present on the surfaces of the silicon substrate and the poly-crystalline silicon film, the silicidation reaction is inhibited in the step of depositing cobalt, with the result that it is possible for the cobalt monosilicide film 117 shown in FIG. 11B not to be formed at all. It should also be noted that, where a cobalt film is deposited after removal of the native oxide film by the pretreatment with a dilute hydrofluoric acid, a nonuniform native oxide film is formed again with time after the pretreatment. As a result, the cobalt monosilicide film 117 is rendered nonuniform as shown in FIG. 12. Further, where only a treatment with a dilute hydrofluoric acid is employed as a pretreatment, a silicon-based oxide film called water mark or water glass is attached to the surfaces of the exposed silicon substrate and the polycrystalline silicon film, particularly to the boundary region with the element isolation film, with the result that the silicidation reaction is inhibited in some cases by the silicon-based oxide film.
Further, the cobalt silicide film is inferior to titanium silicide film in heat resistance. Therefore, a serious problem is brought about such that the cobalt disilicide film 118 is agglomerated as shown in FIG. 13 by the heat in the step of depositing a silicon oxide film after completion of the salicide process, giving rise to elevation of resistance.
On the other hand, various problems are generated in an amorphous silicon/aluminum replacement process which is included in the cobalt salicide process and is intended to decrease the resistance of the contact plug. Let us describe the problems inherent in the amorphous silicon/aluminum replacement process with reference to FIGS. 14A to 14C.
Specifically, interlayer insulating films 112 and 113 are deposited on the structure having a cobalt silicide film 118 as shown in FIG. 11C, followed by forming a contact hole through the interlayer insulating films 112, 113. Then, an amorphous silicon film 119 is deposited. The amorphous silicon film 119 is etched back so as to permit the amorphous silicon film 119 to be left only within the contact hole, followed by depositing an aluminum film 120 and a titanium film 121 on the entire surface, as shown in FIG. 14A.
In the next step, a heat treatment is performed at 600.degree. C. or less among the amorphous silicon film 119, the aluminum film 120 and the titanium film 121 so as to replace the amorphous silicon 119 within the contact hole by an aluminum layer 122. Then, the aluminum film 120 and the titanium film 121 positioned outside the contact hole as well as the silicon 119 sucked out by the replacement reaction are removed by, for example, a CMP process, as shown in FIG. 14B. Further, a wiring metal such as aluminum is deposited on the entire surface, followed by patterning the wiring metal layer so as to form a wiring layer 124 which is connected to the semiconductor element region, as shown in FIG. 14C.
However, a serious problem is generated in the case of forming a contact portion by the process described above. Specifically, an aluminum spike 123 bites the cobalt silicide film 118 in the heating step for replacement of the amorphous silicon with aluminum. In some cases, the spike 123 reaches the diffusion layer. Occurrence of the aluminum spike 123 causes deterioration of the bonding characteristics.
In order to prevent the occurrence of the aluminum spike, it is known to the art to form in advance a titanium nitride film effective as a diffusion barrier within the contact hole. FIGS. 15A to 15C show the process for forming a titanium nitride film in advance in the contact hole.
In the first step, interlayer insulating films 112 and 113 are deposited on the structure having a cobalt silicide film 118 as shown in FIG. 11, followed by forming a contact hole through these insulating films 112, 113. Then, a titanium nitride film 125 and an amorphous silicon film 119 are deposited successively, followed by etching back the amorphous silicon film 119 so as to permit the film 119 to be left only within the contact hole. Further, an aluminum film 120 and a titanium film 121 are deposited on the entire surface, as shown in FIG. 15A.
In the next step, reactions among the amorphous silicon film 119, the aluminum film 120 and the titanium film 121 are carried out by the heating at 600.degree. C. or less so as to replace the amorphous silicon 119 within the contact hole by an aluminum film 122. Then, the aluminum film 120, the titanium film 121 and the titanium nitride film 125, which are positioned outside the contact hole, as well as the silicon 119 sucked out by the replacement reaction, are removed by, for example, a CMP process, as shown in FIG. 15B. Finally, a wiring metal layer 124 such as an aluminum layer is deposited on the entire surface, followed by patterning the wiring metal layer 124 so as to form a wiring layer which is connected to the semiconductor element region, as shown in FIG. 15C.
The process described above makes it possible to prevent an aluminum spike from biting a silicide layer and a diffusion layer below the silicide layer. However, the particular process necessitates an additional step of forming a titanium nitride film. In addition, the titanium nitride film has a high resistivity, leading to elevation of resistance in the contact portion.
As described above, the salicide process using titanium is defective in that, if the gate length is 0.2 .mu.m or less, the resistance is prevented from being lowered sufficiently by the narrow line effect.
The salicide process using cobalt is defective in that the silicidation reaction is inhibited by a native oxide film, and that the silicide is agglomerated in the heating step for depositing interlayer insulating films. The salicide process using cobalt is also defective in that an aluminum spike bites the cobalt silicide layer in the amorphous silicon/aluminum replacement process. In order to prevent generation of the aluminum spike, it is certainly effective to form in advance a titanium nitride film or the like as a diffusion barrier within the contact hole. However, this process necessitates an additional step of forming a titanium nitride film. Also, the presence of the titanium nitride film causes an increased resistance in the contact portion.